Bonding objects together

ABSTRACT

A method of bonding a second object to a first object includes: providing the first object having a thermoplastic liquefiable material in a solid state; providing the second object having a surface portion that has a coupling structure with an undercut, so that the second object is capable of making a positive-fit connection with the first object; pressing the second object against the first object with a tool that is in physical contact with a coupling-in structure of the second object while mechanical vibrations are coupled into the tool; continuing to press and couple vibrations into the tool until a flow portion of the thermoplastic material of the first object is liquefied and flows into the coupling structures of the second object; and letting the thermoplastic material re-solidify to yield a positive-fit connection between the first and second objects by the re-solidified flow portion interpenetrating the coupling structures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/523,724 filed May 2, 2017, which itself is a national stagefiling of PCT/EP2015/075592 filed Nov. 3, 2015, and claims priority toCH 01684/14 filed Nov. 4, 2014, all of which are expressly incorporatedherein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is in the fields of mechanical engineering andconstruction, especially mechanical construction, for example automotiveengineering, aircraft construction, shipbuilding, machine construction,toy construction etc.

Description of Related Art

In the automotive, aviation and other industries, there has been atendency to move away from steel constructions and to use lightweightmaterial such as aluminum or magnesium metal sheets or polymers, such ascarbon fiber reinforced polymers or glass fiber reinforced polymers orpolymers without reinforcement, for example polyesters, polycarbonates,etc. instead.

The new materials cause new challenges in bonding elements of thesematerials—especially in bonding flattish object to another object.

To meet these challenges, the automotive, aviation and other industrieshave started heavily using adhesive bonds. Adhesive bonds can be lightand strong but suffer from the disadvantage that there is no possibilityto long-term control the reliability, since a degrading adhesive bond,for example due to an embrittling adhesive, is almost impossible todetect without entirely releasing the bond.

FR 1 519 111 teaches a method of fastening a screw or similar fixationelement to a thermoplastic body by applying high-frequency vibration toit to displace thermoplastic matter and cause it to flow in an interiorcavity of the fixation element. U.S. Pat. No. 5,271,785, FR 2,112,523,U.S. Pat. Nos. 3,184,353, 3,654,688, and GB 1,180,383 teach securing ametallic body to a thermoplastic body by bringing the bodies intocontact and subjecting the metallic body to mechanical vibration untilthermoplastic material of the thermoplastic body liquefies, the metallicbody is essentially fully enwrapped in the thermoplastic body, andthermoplastic material flows into recesses of the metallic body. All ofthese methods are suitable only for anchoring a metallic part in a deepthermoplastic object, and the required energy input and correspondingimpact on the parts to be connected is substantial.

US 2010/0079910 teaches manufacturing an electronic device with aplastic housing part and a metallic housing part, wherein the plastichousing part is attached to the metallic housing part by an ultrasonicbond. The applications of the concept taught in US 2010/0079910 arelimited.

A further concept of prior art approaches includes shaping thethermoplastic body to include a flange-like protrusion into which afastening element, such as a nut, is pressed. This concept, however, hasthe disadvantage of being more complex, as shaping plastic parts thatotherwise may have a simple, for example sheet-like, form with a flange,which depending on the application needs to have a precisely definedposition, may drastically increase the manufacturing cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of bondingtwo objects together, the method overcoming drawbacks of prior artmethods and being especially suited for bonding a second object to afirst object of a polymer-based material. It is a further object toprovide equipment for carrying out the method.

According to an aspect of the invention, a method of bonding a secondobject to a first object, the method including the steps of:

-   -   providing the first object, the first object including a        thermoplastic liquefiable material in a solid state;    -   providing the second object, the second object including a        surface portion that has a coupling structure with an undercut,        and/or in which the second object, as described hereinafter, is        capable of being deformed to include such a coupling structure        with an undercut, whereby the second object is capable of making        a positive-fit connection with the first object;    -   pressing the second object against the first object by a tool        that is in physical contact with a coupling-in structure of the        second object while mechanical vibrations are coupled into the        tool,    -   continuing the step of pressing and coupling vibrations into the        tool until a flow portion of the thermoplastic material of the        first object is liquefied and flows into the coupling structures        of the second object,    -   letting the thermoplastic material of the first object        re-solidify to yield a positive-fit connection between the first        and second objects by the liquefied and re-solidified flow        portion interpenetrating the coupling structures.

The liquefaction of the flow portion in this is primarily caused byfriction between the vibrating second object and the surface of thefirst object, which friction heats the first object superficially.

A special property of the approach according to many embodiments of theinvention is therefore also that the flow portion that has beengenerated in a contact zone between the first and second objects mayimmediately flow into existing cavities of the second object, andthereby the zone that is influenced by the heat generated during theprocess remains small, for example essentially restricted to theintermixing zone.

The flow behavior of the flow portion will be influenced by the factthat due to the approach according to the present invention, a materialflow is generated towards the surface of the non-liquefiable material(i.e. the second object; convergent flow), to which surface, by thevibrations and friction, heat is continuously supplied. Thus, generallylittle heat will flow away. Therefore, a large penetration depth ofthermoplastic material into the coupling structures becomes achievableeven after a short process time, the flow not being stopped by heat lossof liquefied material coming into contact with cold spots. This is incontrast for example to the “Woodwelding” process as, for example,described in WO 98/42988 where there is a divergent flow by liquefiedmaterial flowing away from the interface zone and thus transporting heataway into structures that have remained cold.

The first and second objects are construction components (constructionelements) in a broad sense of the word, i.e. elements that are used inany field of mechanical engineering and construction, for exampleautomotive engineering, aircraft construction, shipbuilding, buildingconstruction, machine construction, toy construction, etc. Generally,the first and second objects will both be artificial, man-made objects,and at least the first object will include artificial material; theadditional use of naturally grown (non-living matter) material, such aswood-based material, in the first and/or second object is not excluded.

The materials of the first object and of the second object may behomogeneous or inhomogeneous. For example, the first object may have thethermoplastic material and in addition include other, non-liquefiablematerial, and/or it may have a plurality of layers of thermoplasticmaterial of different compositions. Similarly, the second object mayinclude different portions of different materials, as explained in moredetail hereinafter. Additionally or as an alternative, in embodiments,the second object may be caused to penetrate through a plurality ofobjects (the first object plus at least one further object) to securethe plurality of objects to each other, as also explained in more detailhereinbelow.

The coupling-in structure may be a coupling-in face, especiallyconstituted by a proximal-most end face, with or without guidingstructures (such as a guiding hole for an according protrusion of thetool), for a separate sonotrode that serves as the tool. In alternativeembodiments, the coupling-in structure may include a coupling thatcouples the second object directly to a vibration generating apparatus,which vibration generating apparatus then serves as the tool. Such acoupling may for example be by a thread or a bayonet coupling orsimilar. Thus in these embodiments, the second object is at the sametime a sonotrode coupled to a vibration generating apparatus.

In other embodiments, the tool is a sonotrode fastened to a vibrationgenerating apparatus. Sonotrodes of this kind are for example known fromultrasonic welding.

In even further embodiments, the tool may be an intermediate piece(different from the first object), against which intermediate piece asonotrode presses and which is of a material that does not liquefy underthe conditions that apply during the process. Generally, the approachaccording to aspects of the invention excludes that the vibrations arecoupled into second object only via first object; rather a physicalcontact between the second object and the vibrating tool is required.

The flow portion of the thermoplastic material is the portion of thethermoplastic material that during the process and due to the effect ofthe mechanical vibrations is caused to be liquefied and to flow.

The coupling structures of the second object are of a material that isnot liquefiable. As explained in more detail hereinafter, thisdefinition includes the possibility that the material is liquefiable ata substantially higher temperature than the material of the firstobject, such as a temperature higher by at least 50°. In addition or asan alternative, the condition may hold that at a temperature at whichthe first object's thermoplastic material is flowable, the viscosity ofthe material of the second object is higher than the viscosity of thethermoplastic material of the first object by orders of magnitude, forexample by at least a factor between 10³ and 10⁵. In addition or as analternative to including a different liquefiable matrix material with adifferent liquefaction temperature and/or different glass transitiontemperature, this can also be achieved by a higher filling grade of forexample a fiber filler.

Coupling structures may include sequences of radial protrusions andindentations (such as ribs/grooves), an open porous foam-like structure,openings open to the distal side, which openings define an undercut bybeing widened, at least into one lateral direction, towards a proximalside, etc. Any structure that defines an undercut with respect to axialdirections is suitable.

In coupling structures that include sequences of radial protrusions andindentations (for example around an outer surface of a portion of thesecond object or along an interior surface of the second object), ddepth of the intermixing zone may be defined as radial depth into whichthe flow portion penetrates starting at outermost protrusions, Incoupling structures that include an open porous structure, the depth ofthe intermixing zone may be defined as the depth of the open porousstructure into which the thermoplastic material penetrates starting atthe surface of the open porous structure, measured perpendicularlythereto. Similarly, in coupling structures that include openings open tothe distal side the depth of the intermixing zone may be defined as thedepth into which the thermoplastic material penetrates starting at thedistally facing surface.

Especially, in embodiments the mechanical vibration transmitting partsof the second object consist of metal and/or other hard materials(glasses, ceramics, etc.) and/or thermosetting plastics and/orthermoplastics that remain below their glass transition temperatureduring the entire process.

In a special group of embodiments, the second object includes a secondthermoplastic material having a liquefaction temperature substantiallyhigher than the liquefaction temperature of the first objectthermoplastic material. Then, after the step of causing a flow portionof the thermoplastic material of the first object is liquefied, thesecond object may be pressed against a support or a non-liquefiableportion of the first object while coupling vibrations into the secondobject is continued (with a same or a higher or possibly even a lowerintensity than initially) until a second flow portion of the secondthermoplastic material is liquefied and leads to a deformation of thesecond object. Especially, this further method step may be carried outas described in WO 2015/117253, incorporated herein by reference, untila foot portion and/or a head portion of the second object is created forbonding the first and second objects together by an additional riveteffect.

While embodiments of this special group of embodiments include thesecond object, after the bonding process, reaching through the firstobject to the distal side, in an alternative group of embodiments thedistal side is left intact, i.e. an intermixing zone that includesportions of the first and second objects does not reach to the distalside.

In embodiments, the second object is anchored in a depth-effectivemanner by providing the second object with an anchoring portion thatextends along the anchoring axis, optionally with structure elementsthat are arranged on a peripheral surface of the second object and/oralong an inner surface of an axially extending portion of the secondobject.

In embodiments, especially the penetration depth, by which the secondobjects penetrates into the first object, i.e. the axial extension ofthose parts of the second object that penetrate into the first object,is larger (for example substantially larger) than a depth of theintermixing zone, i.e. the zone in which both, portions of the first andsecond object are present after the bonding process. In other words, inthese embodiments including depth-effective anchoring, a width of theone part of the second object that penetrates into the first object inat least one lateral dimension, and often in both lateral dimensions, issmaller than the penetration depth by which the second object penetratesinto the first object. The depth of the intermixing zone is then definedas the characteristic depth of the structure elements on the peripheralsurface, i.e., a depth measured perpendicular to the anchoring axis.

Embodiments of a group include, in addition or as an alternative toincluding depth-effective anchoring, a bonding surface with a pluralityof structure elements that are spaced laterally from each other and/orpossibly form an extended, for example circumferential, groove, thebonding surface following a surface portion of the first object. Forexample, if the first object is planar, the structure elements willextend along a plane.

Embodiments, for example embodiments that include a depth-effectiveanchoring, may include providing a bore in the first object prior to thestep of pressing, and in the step of pressing, a part of the secondobject is pressed into the bore. In this, a bore diameter is preferablychosen to be less than an outer diameter of the part pressed into thebore. Such a bore may be a blind hole or a through bore. Also anchoringin other indentations such as grooves etc. is possible.

A through bore may also be advantageous in embodiments, in which thesecond object is comparably thin, such as a thermoplastic sheets. Themethod of bonding a second object to the first object may then includelining the through bore with the second object, for example for thepurpose of fastening a further object thereto, to serve as afeedthrough, serve as barrier that is crossable under pre-definedconditions only (as is the case for a septum or for a second object witha removable cover or similar) or have another purpose. In embodiments ofthis special category, the thickness of the first object may correspondto 2-40 times or 2-20 times, especially between 3 times and 10 times theinterpenetration depth (depth of the intermixing zone).

In accordance with an even further group of embodiments, the bonding iscarried out in a “planar bond” or “flattish bond” manner, with acomparably small penetration depth. This group of embodiments mayespecially be suited also for bonding a second object to a first objectthat is comparably thin or that is sensitive to damages or has highrequirements for leaving other surfaces than the one to which the secondobject is bonded intact.

In embodiments of this group, the second object includes a plurality ofstructure elements for the liquefied material to flow into, whichstructure elements are spaced laterally from each other, i.e. extendalong a plane which during the anchoring is parallel to a surface planeof the first object or, if the case may be, extend along another,non-planar surface of the first object. Especially, the bond between thefirst and second object may be a planar bond, wherein the area of theinterface between the first and second object is essentially parallel tothe surface plane of the first object and has, at least in onedimension, preferably in both in-plane dimensions, substantially greaterthan the penetration depth, for example greater by at least a factor 2or 3, at least a factor 5, or at least a factor 10. In this, thepenetration depth may be equal to the depth of the intermixing zone ormay be smaller than the latter.

Embodiments that include bonding with a small penetration depth comparedto the depth of the intermixing zone may also include bonding of thesecond object to a not planar surface portion of the first object. Forexample, the first object may have a certain proximally facing surfacecontour, and the second object may have an overall shape following thiscontour or may be deformable to do so.

Alternatively, the first object may have a countersunk or opening oropening provided with another structure along its periphery, wherein thesecond object has an accordingly adapted (for example conical if theopening is countersunk) shape. In embodiments where the first object iscomparably thin and there are requirements for the distal surface, thestructure elements of the second object may in such embodiments adaptedto the depth. Especially, the relative sizes of the structure elementsmay decrease towards distally, so that their capacity to accommodateflowable material decreases towards the distal side, and accordinglydoes the heat impact.

In embodiments, a design criterion is that the volume of structureelements (such as indentations or pores) into which the liquefiedmaterial can flow is larger than the displaced volume. This leads to acriterion for embodiments of the invention according to which along thesurface parts that include the coupling structures the porosity is atleast 50% for a certain depth. The porosity here is defined as afraction that empty spaces take up of the total volume, measured from anouter convex hull to a certain depth (corresponding to a depth of theintermixing zone, measured in axial direction); it may apply also tomacroscopic structures that are not necessarily viewed as “pores”. Ifthis optional design criterion is fulfilled, no volume has to bedisplaced to the surface or sideways or similar.

More in general, in embodiments, the method may include causing the flowportion to flow into the indentations and/or pores and preventing theflow portion from flowing to regions laterally of the second object.

To this end, optionally, in addition to providing an indentation/porevolume satisfying the above condition, the method may also includepressing a (non-vibrating) retaining device against proximal surface ofthe first object in a vicinity of the second object, for example aroundthe interface between the first and second objects. Such a retainingdevice may prevent bulges or the like around the location where thesecond object is anchored in the first object.

In embodiments of this group of “planar bond” or other “flattish bond”anchoring, the second object in addition to cavities(indentations/pores) includes a distal protruding structure that may forexample serve as energy director. Especially, such distal protrudingstructure may have a shape with a portion that tapers towards the distalside, for example ending in a tip or edge or rounded distal end. In thiscase, a lateral distance between the distal protruding structure and thecavity accommodating the flow portion may be minimal. Especially, anyspacing between such distal protruding structure and the cavity may beavoided, so that the overall shape of the second object at the distalsurface is undulated between the distal protrusion and cavity.

In embodiments of all groups described hereinbefore, the couplingstructures that include an undercut with respect to axial(proximodistal) directions and thereby make a positive-fit connectionpossible, are pre-manufactured properties of the second object.

In addition or as an alternative, the second object may include adeformable portion, and the method may include making a structure for apositive-fit connection during the process of pressing the second objectagainst the first object while mechanical vibrations are coupled intothe second object.

For example, the second object may include a plurality of deformablelegs or a deformable collar extending in a substantially axial directionas a deformable structure. During the process, the deformable structureis bent away from the axial direction so that after re-solidification anundercut is formed.

Embodiments using this principle of deformation may feature theadvantage that the effective anchoring area may, due to the deformation,be larger than the surface area portion of the first object penetratedby the second object, i.e. the footprint may be enlarged compared to anembodiment without the deformation.

A further possible advantage is that, for example, a lightweightdeformable material may be used for the deformable portion. Especially,a material may be used that is deformable at the temperature at whichthe process takes place but that exhibits substantial stiffness at roomtemperature (or, more generally, the temperature at which the assemblywill be used). For example, the deformable portion may be of athermoplastic material with a glass transition temperature that issubstantially higher than the glass transition temperature of the firstobject thermoplastic material of which the flow portion is formed.

In a specific embodiment, of this principle, PBT (Polybutyleneterephthalate) was used as the first object thermoplastic material,which material becomes flowable at temperatures of about 180° C., andPEEK was used as a material of the second object's portion that includesthe deformable portion. PEEK is not liquid/flowable at 180° C. but isabove its glass transition temperature (being about 140° C.).

More in general, in embodiments in which the deformable portion includesa thermoplastic material, it may be advantageous if the glass transitiontemperature of the deformable portion is between the glass transitiontemperature of the first object thermoplastic material and thetemperature at which the thermoplastic material becomes sufficientlyflowable.

In this text, the liquefaction temperature or the temperature at which athermoplastic material becomes flowable is assumed to be the meltingtemperature for crystalline polymers, and for amorphous thermoplastics atemperature above the glass transition temperature at which the becomessufficiently flowable, sometimes referred to as the ‘flow temperature’(sometimes defined as the lowest temperature at which extrusion ispossible), for example the temperature at which the viscosity drops tobelow 10⁴ Pa*s (in embodiments, especially with polymers substantiallywithout fiber reinforcement, to below 10³ Pa*s).

For applying a counter force to the pressing force, the first object maybe placed against a support, for example a non-vibrating support.According to a first option, such a support may include a supportingsurface vis-à-vis the spot against which the first object is pressed,i.e. distally of this spot. This first option may be advantageousbecause the bonding can be carried out even if the first object byitself does not have sufficient stability to withstand the pressingforce without substantial deformation or even defects.

In embodiments that include deforming the second object during theprocess of pressing the second object against the first object, thesupport may include a shaping feature that assists the deformationprocess. For example, the support may be shaped to have a shapingprotrusion or shaping indentation, to cause an outward bending or inwardbending of the deformable structure, respectively.

It is further possible that the method uses a cooling effect by thesupport on the thermoplastic material of the first object, whereby thethermoplastic material of the first object is kept at a coolertemperature and thus remains harder at an interface to the support.Thereby, the deformable structure will be caused to deform such as notto get too close to the interface with the support.

According to a second option, the distal side of the first object may beexposed, for example by the first object being held along the lateralsides or similar. This second option features the advantage that thedistal surface will not be loaded and will remain unaffected if thesecond object does not reach to the distal side.

In embodiments, the first object is placed against a support with noelastic or yielding elements between the support and the first object,so that the support rigidly supports the first object.

In a group of embodiments, the second object includes an inner portionand an outer portion, with a gap therebetween. Then, the couplingstructures of the second object may include outer structures of theinner portion and/or inner structures of the outer portion and/or outerstructures of the outer portion, and the step of causing a flow of theflow portion includes causing a flow into the gap.

According to an option, inner and outer portions may together be of onepiece.

In a group of embodiments, the second object includes a first portion ofa first material and a second portion of a second material. This groupof embodiments, for example, may make possible to save cost if the firstportion includes critical sections, such as a thread or other structurefor connecting a further element to the assembly of the first and secondobjects, is made of a high-quality building material, for examplestainless steel, titanium, aluminum, copper, etc., whereas the secondportion may include a lower cost material and primarily serve forstabilization of the second object with respect to the first object.

Especially, if the second object includes an inner portion and an outerportion, the inner portion may be of the first material and the outerportion may be of the second material. Thereby, by the flow of the flowportion into the gap, the second object itself is also stabilized, inaddition to being bonded to the first object.

Embodiments that include a first portion of a first material and asecond portion of a second material may, for example, includeembodiments of the above-discussed group that include a deformableportion. In these, the deformable portion may, for example, belong tothe second portion of a second material, and mounting structure formounting a further object to the first object or for another functionmay be of another, not deformable material, such as of a hard metal.

An further advantage of embodiments with a first and a second material(in addition to optionally including a deformable portion, with theabove-discussed advantages) is that they provide the possibility ofusing a lightweight and/or low cost material for those parts of thesecond object that use up a lot of space (for example, to yield asufficiently large footprint in the above sense) while maintaining thepossibility of having a sufficiently stable/stiff functional piece, forexample with a thread or other functional structure, constituted by thefirst portion.

If the second material is itself capable of being deformed and possiblycapable of flowing, at temperatures above the liquefaction temperatureof the first object material, this approach may feature the even furtheradvantage that the first and second portions may optionally be assembledin situ if they are initially not connected with each other or onlyloosely connected. For example, the second material may flow relative tothe first material to embed a part of the first portion, for example ina positive-fit like manner.

In a group of embodiments, the second object may constitute a mountingpiece (mounting pillar, mounting plug, etc.) for mounting a furtherobject to the first object. Especially, an inner portion of theabove-described kind may include a mounting structure, such as a threador bayonet fitting structure or guide bushing or snap-on structure, etc.The outer portion may serve as a fastening flange for fastening themounting structure. Compared to prior art fastening flanges, thisapproach has substantial advantages:

Instead of two separate steps for providing a fastening flange and formounting the fastening element to the fastening flange, the entirestructure may be attached in one single step.

The positioning of the mounting piece may optionally be done directly atthe otherwise completed first object, for example after the latter hasbeen placed relative to further parts and/or for example in presence ofthe further object. Thus, during the manufacturing of the first objectitself, there is no need for a precise alignment step. Therefore, theprecision of the positioning in relation to the end product may bedrastically increased.

Due to the approach according to the invention, anchoring of themounting structure is effective also in situations where the firstobject is comparably thin and/or where another, distal surface of thefirst object needs to remain unaffected. This is in contrast to theabove-discussed prior art approaches that include plunging a metallicbody (threaded bush or the like) in a thermoplastic object.

Especially, in embodiments the second object includes a proximal bodyand, distally thereof, a plurality of distal extensions that in the stepof pressing are pressed into the first object. Especially, the distalextensions may include at least one outer extension and at least oneinner extension.

For example, the proximal body may include a portion in theabove-mentioned sense of a second material, and, embedded therein, aportion of a first material, which portion of the first material isaccessible from the proximal side also after the step of letting thethermoplastic material re-solidify, and which may have the mountingstructure. The portion of the first material may extend distally to format least one of the distal extensions (such as a central protrusion) ormay be restricted to the proximal side.

In a group of embodiments, the first object is a flattish object, suchas a polymer plate, for example a polymer cover.

The bond between the second object and the first object may have anypurpose of a bond between two objects. For example, in the automotive oraviation industries, the bond may be a bond between a structural elementof plastic (first object) and a metallic or compound material structuralelement.

In a group of embodiments, the second object may be an anchor in thefirst object for fastening a further element thereto.

In another group of embodiments, the second object may be a connectorthat bonds a further, third object to the first object by the methoddescribed herein. These embodiments thus concern:

A method of connecting a third object to a first object by bonding asecond object to the first object and thereby securing the third objectto the first object, the method including the steps of:

-   -   providing the first object, the first object including a        thermoplastic liquefiable material in a solid state;    -   providing the third object;    -   providing the second object, the second object including a        surface portion that has a coupling structure with an undercut        and/or is capable of being deformed to include such a coupling        structure with an undercut, whereby the second object is capable        of making a positive-fit connection with the first object;    -   arranging the third object relative to the first object,    -   pressing the second object against the first object by a tool        that is in physical contact with a coupling-in structure of the        second object while mechanical vibrations are coupled into the        tool,    -   continuing the step of pressing and coupling vibrations into the        tool until a flow portion of the thermoplastic material of the        first object is liquefied and flows into the coupling structures        of the second object,    -   letting the thermoplastic material of the first object        re-solidify to yield a positive-fit connection between the first        and second objects by the liquefied and re-solidified flow        portion interpenetrating the coupling structures,    -   wherein the step of pressing the second object against the first        object is carried out until the second object is in physical        contact with the third object and secures the third object to        the first object.

Especially, in the step of arranging the third object relative to thefirst object, the third object may be placed proximally of the firstobject, and after the step of arranging, the second object may be causedto penetrate the third object until a distal portion thereof reaches thefirst object for the second object to be pressed against the firstobject.

For example, to this end, the third object may be of a liquefiablethermoplastic material or otherwise penetrable material for the secondobject to penetrate through the third object until its distal portionreaches the first object.

Then, it is further possible to arrange the coupling structure of thesecond object in a manner that a positive-fit connection is also causedwith the third object, in addition to the connection with the firstobject.

In addition or as an alternative, the third object may include a borethrough which the distal portion of the third object is guided to reachthe first object.

For securing the third object to the first object, the second object mayinclude a head or bridge portion that rests against a proximally facingsurface portion of the third object while the distal portion of thesecond object is anchored in the first object.

In addition or as an alternative, if the third object includesthermoplastic material, a positive-fit connection between the second andthird objects may be caused by material of the third object penetratinginto structures of the second object, in addition to material of thefirst object interpenetrating the coupling structures.

In addition or as yet another alternative, thermoplastic material of thethird object may be caused to be welded to thermoplastic material of thefirst object by the effect of the second object being pressed into theassembly of the third and first objects or may be caused tointerpenetrate flowable material of the first object in a non-mixingmanner to yield a mechanical and/or adhesive connection after there-solidification.

It is even an option that material of the third object that is bonded tothe first object includes an elastomeric material or other material,even if such material is not liquefiable, and even if nopre-manufactured opening is present. Especially, a cutting portion ofthe second object may pierce through a portion of the third object untilit comes into contact with the first object placed distally thereof.

In this way (bonding of not meltable or meltable soft material to athermoplastic first object), connections between hard and soft materialsbecome possible, that for example cannot be processed together inhard/soft injection molding. An example would be the bonding of adamping cushion (third object) to a thermoplastic first object, such asa thermoplastic sheet.

In a group of embodiments, the second object comprises, at the surfacethat during the pressing and vibrating is in direct contact with thefirst object, structures serving as energy directors, such as edges ortips. While for ultrasonic welding and also for the “Woodwelding”process as for example described in WO 98/42988 or WO 2008/080 238,energy directors are known, they will generally be present on the objectof the material to be liquefied. Embodiments of the present invention,however, reverse this by providing energy directors on material that isnot liquefied but is interpenetrated by liquefied material.

The invention also concerns a connecting element for being secured, in amethod as described in this text, to a first object that includes athermoplastic material. More in particular, any properties of secondobjects that are described and/or claimed referring to the method may beproperties of the connecting element and vice versa.

In this text the expression “thermoplastic material being capable ofbeing made flowable e.g. by mechanical vibration” or in short“liquefiable thermoplastic material” or “liquefiable material” or“thermoplastic” is used for describing a material including at least onethermoplastic component, which material becomes liquid (flowable) whenheated, in particular when heated through friction i.e. when arranged atone of a pair of surfaces (contact faces) being in contact with eachother and vibrationally moved relative to each other, wherein thefrequency of the vibration has the properties discussed hereinbefore. Insome situations, for example if the first object itself has to carrysubstantial loads, it may be advantageous if the material has anelasticity coefficient of more than 0.5 GPa. In other embodiments, theelasticity coefficient may be below this value, as the vibrationconducting properties of the first object thermoplastic material do notplay a role in the process since the mechanical vibrations aretransferred directly to the second object by the tool.

Thermoplastic materials are well-known in the automotive and aviationindustry. For the purpose of the method according to the presentinvention, especially thermoplastic materials known for applications inthese industries may be used.

A thermoplastic material suitable for the method according to theinvention is solid at room temperature (or at a temperature at which themethod is carried out). It preferably includes a polymeric phase(especially C, P, S or Si chain based) that transforms from solid intoliquid or flowable above a critical temperature range, for example bymelting, and re-transforms into a solid material when again cooled belowthe critical temperature range, for example by crystallization, wherebythe viscosity of the solid phase is several orders of magnitude (atleast three orders of magnitude) higher than of the liquid phase. Thethermoplastic material will generally include a polymeric component thatis not cross-linked covalently or cross-linked in a manner that thecross-linking bonds open reversibly upon heating to or above a meltingtemperature range. The polymer material may further include a filler,e.g. fibres or particles of material that has no thermoplasticproperties or has thermoplastic properties including a meltingtemperature range that is considerably higher than the meltingtemperature range of the basic polymer.

In this text, generally a “non-liquefiable” material is a material thatdoes not liquefy at temperatures reached during the process, thusespecially at temperatures at which the thermoplastic material of thefirst object is liquefied. This does not exclude the possibility thatthe non-liquefiable material would be capable of liquefying attemperatures that are not reached during the process, generally far (forexample, by at least 80° C.) above a liquefaction temperature of thethermoplastic material or thermoplastic materials liquefied during theprocess. The liquefaction temperature is the melting temperature forcrystalline polymers. For amorphous thermoplastics the liquefactiontemperature (also called “melting temperature in this text”) is atemperature above the glass transition temperature at which the becomessufficiently flowable, sometimes referred to as the ‘flow temperature’(sometimes defined as the lowest temperature at which extrusion ispossible), for example the temperature at which the viscosity drops tobelow 10⁴ Pa*s (in embodiments, especially with polymers substantiallywithout fiber reinforcement, to below 10³ Pa*s)), of the thermoplasticmaterial.

For example, the non-liquefiable material may be a metal, such asaluminum or steel, or wood, or a hard plastic, for example a reinforcedor not reinforced thermosetting polymer or a reinforced or notreinforced thermoplastic with a melting temperature (and/or glasstransition temperature) considerably higher than the meltingtemperature/glass transition temperature of the liquefiable part, forexample with a melting temperature and/or glass transition temperaturehigher by at least 50° C. or 80° C.

Specific embodiments of thermoplastic materials are: Polyetherketone(PEEK), polyesters, such as polybutylene terephthalate (PBT) orPolyethylenterephthalat (PET), Polyetherimide, a polyamide, for examplePolyamide 12, Polyamide 11, Polyamide 6, or Polyamide 66,Polymethylmethacrylate (PMMA), Polyoxymethylene, orpolycarbonateurethane, a polycarbonate or a polyester carbonate, or alsoan acrylonitrile butadiene styrene (ABS), anAcrylester-Styrol-Acrylnitril (ASA), Styrene-acrylonitrile, polyvinylchloride, polyethylene, polypropylene, and polystyrene, or copolymers ormixtures of these.

In embodiments in which both, the first and the second object includethermoplastic material, the material pairing is chosen such that themelting temperature of the second object material is substantiallyhigher than the melting temperature of the first object material, forexample higher by at least 50°. Suitable material pairings are forexample polycarbonate or PBT for the first object and PEEK for thesecond object.

In addition to the thermoplastic polymer, the thermoplastic material mayalso include a suitable filler, for example reinforcing fibers, such asglass and/or carbon fibers. The fibers may be short fibers. Long fibersor continuous fibers may be used especially for portions of the firstand/or of the second object that are not liquefied during the process.

The fiber material (if any) may be any material known for fiberreinforcement, especially carbon, glass, Kevlar, ceramic, e.g. mullite,silicon carbide or silicon nitride, high-strength polyethylene(Dyneema), etc.

Other fillers, not having the shapes of fibers, are also possible, forexample powder particles.

Mechanical vibration or oscillation suitable for the method according tothe invention has preferably a frequency between 2 and 200 kHz (evenmore preferably between 10 and 100 kHz, or between 20 and 40 kHz) and avibration energy of 0.2 to 20 W per square millimeter of active surface.The vibrating tool (e.g. sonotrode) is, e.g., designed such that itscontact face oscillates predominantly in the direction of the tool axis(longitudinal vibration) and with an amplitude of between 1 and 100 μm,preferably around 30 to 60 μm. Such preferred vibrations are, e.g.,produced by ultrasonic devices as, e.g., known from ultrasonic welding.

In this text, the terms “proximal” and “distal” are used to refer todirections and locations, namely “proximal” is the side of the bond fromwhich an operator or machine applies the mechanical vibrations, whereasdistal is the opposite side. A broadening of the connector on theproximal side in this text is called “head portion”, whereas abroadening at the distal side is the “foot portion”. The “axis” is theproximodistal anchoring axis along which the pressure in the step ofpressing is applied. In many embodiments, the mechanical vibrations arelongitudinal vibrations with respect to the axis.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, ways to carry out the invention and embodiments aredescribed referring to drawings. The drawings are schematic in nature.In the drawings, same reference numerals refer to same or analogouselements. The drawings, unless otherwise specified, show views of crosssections along a plane parallel to the anchoring axis (“vertical” crosssections). The drawings show:

FIGS. 1a-1d stages of an bonding process according to a first embodimentof the invention;

FIG. 2 an alternative configuration for a bonding process similar to theprocess of the first embodiment;

FIGS. 3a and 3b a bonding process with an alternative second object;

FIG. 4a a view, from the distal side, of a second object;

FIG. 4b a cross section of a second object similar to the one of FIG. 4a;

FIG. 4c the second object of FIG. 4b anchored in a first object;

FIG. 4d a further variant of a second object;

FIGS. 5a and 5b a bonding process with alternative first and secondobjects;

FIGS. 6a-6d a bonding process according to yet a further embodiment;

FIG. 7a a hybrid second object for the process of FIGS. 6a -6 d;

FIG. 7b , in partial cross section, a further hybrid second object;

FIG. 7c , again in partial cross section, the second object of FIG. 7cafter the process;

FIG. 7d a further hybrid second object, useable for bonding processeswithout any foot portion formation;

FIGS. 8 and 9 further embodiments of second objects;

FIG. 10 a further bonding process with an alternative second object;

FIGS. 11-16 further embodiments for bonding a second object to a flatfirst object;

FIGS. 17a-17b a boding process of a second object with a deformablesection to a first object;

FIGS. 18-20 variants of such a process;

FIGS. 21a and 21b bonding a third object to the first object by thesecond object;

FIGS. 22 and 23, alternative second objects for such a bonding process;

FIGS. 24a and 24b , a top view of a semifinished product for forming yetanother second object, and a view of a section through the second objectformed thereof;

FIGS. 25 and 26 views of yet further second objects;

FIG. 27 a schematical horizontal section through a further secondobject;

FIG. 28 a bottom view of a cap element of such a second object;

FIGS. 29a and 29b a process of bonding a foam material to athermoplastic first object;

FIG. 30 a further arrangement for bonding a second object to a firstobject;

FIG. 31 a variant of a second object;

FIG. 32 an even further process of bonding a second object to a firstobject;

FIGS. 33, 34 and 35 variants of this process;

FIG. 36 another second object for being bonded to a first object; and

FIG. 37 an even further second object for being bonded to a firstobject.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a depicts a basic set-up of embodiments of the invention. Thefirst object 1 consists of a thermoplastic material, for example ofpolybutylene terephthalate (PBT), compact or foamed, or polycarbonate orAcrylonitrile butadiene styrene or any other thermoplastic polymer thatis solid at room temperature and, for example, has a melting temperatureof less than 250° C.

The second object is, for example, metallic or of plastic (thermosettingor thermoplastic). If the second object is liquefiable, the liquefactiontemperature is such that it is not flowable at temperatures at which thefirst thermoplastic is flowable. For example, the melting temperature ofthe second object material is higher than the melting temperature of thefirst material by at least 50° or at least 80° C.

The second object has a structure capable of making a positive-fitconnection with material of the first object after the latter has flown.More in particular, the second object has a surface portion that has anundercut with respect to axial directions (axis 10). For example, thesurface structure includes at least one rib 4 running in a non-axialdirection or at least one hump. In the depicted embodiment the secondobject is assumed to be rotationally symmetrical about the axis 10 andincludes a plurality of circumferential ribs 4 between which grooves 5are formed.

At the distal end, the second object has a tip 3, and at the proximalend, a head portion 6 forms a proximally facing coupling face for themechanical vibrations.

A sonotrode 7 is used to press the second object against the firstobject while mechanical vibrations are coupled into the second object.As shown in FIG. 1b , liquefaction of material of the first object setsin starting at the interface to the tip 3. The continued pressing of thesecond object into the first object will cause the second object to bemoved relative to the first object in the direction of the block arrows.A flow 11 of liquefied thermoplastic material of the first object setsin.

FIG. 1c shows the configuration towards the end of the process. Becausethe first object will only be liquefied in a vicinity of the surface ofthe second object but will remain solid and thus exhibit some stiffnesselsewhere, the liquefied material cannot evade arbitrarily, the pressingof the second object into the first object will generate somehydrostatic pressure on the first object, and this will cause the flow11 to immediately fill the undercut structures, such as the grooves 5.

After the vibrations have stopped, the liquefied thermoplastic materialwill again solidify, leaving the second object solidly anchored in thefirst object (FIG. 1d ).

FIG. 1d also illustrates the penetration depth d_(p) and the depth d_(i)of the intermixing zone (interpenetration depth) which latter is thedepth into which the flow portion penetrates starting at outermostsurface features of the second object, here the depth d_(i) of theintermixing zone corresponds to the depth of the grooves 5. As can beseen in FIG. 1d , in these embodiments with depth-effective anchoring,the penetration depth is substantially larger than the depth of theintermixing zone.

FIG. 1d also shows the width w of the portion of the second object thatpenetrates into the first object. Clearly, the width is smaller than thepenetration depth, as is a further possible characteristic ofembodiments of depth-effective anchoring.

The second object in this and other embodiments described in this textmay have the function of serving as a connector, (nut, threaded bolt,etc.) feedthrough, bushing, other connector etc.

In FIGS. 1a-1d , it is assumed that the second object 2 is pushedthrough a surface of the first object 1 (similar considerations apply ifon top of the first object, a further, third object is placed, asdiscussed in more detail hereinafter, for example referring to FIGS. 21a/21 b, 29 a/29 b, 30). During the process, a volume corresponding to thevolume of an anchoring portion of the second object (here: the shaft,i.e. the second object without the head portion 6) is displaced, forexample to proximal directions and/or the introduction of the secondobject causes a slight deformation of the whole first object.

In cases where:

-   -   such displacement and/or deformation is undesired and to be kept        at a minimum, and/or    -   due to the shape/dimensions of the second object and/or        resistance of the first object it is difficult to push the        second object through a surface of the first object, and/or    -   guidance of the second object during introduction merely by the        sonotrode and/or external means is difficult,    -   it is and option to provide the first object with a bore 20        prior to the step of pressing the second object against the        first object. This is, again schematically, illustrated in FIG.        2.

For the diameter d_(h) of the bore, the following considerations mayapply (not only for shapes like the one shown in FIG. 2 but generallyfor a part of the second object that during the process is pressed intoa bore):

-   -   The diameter d_(h) of the bore should be smaller than an outer        diameter d₂ of protruding structures of the anchoring portion of        the second object (the ribs 5 in the depicted embodiment).        Exceptions to this principle can be envisaged for non-circular        symmetric geometries.    -   In most embodiments, the diameter d_(h) of the bore should be        chosen such that the volume of the bore is equal to or smaller        than the volume taken up by the anchoring portion. In other        words, the bore diameter in these embodiments should be chosen        such that the volume of displaced portions of the thermoplastic        first object material is at approximately equal to or larger        than the volume of structures into which the displaced volume        can flow. However, especially in embodiments where the coupling        structures are defined by an open porous structure of the second        object, into which the flowable material flows against some        resistance, this need not be the case.    -   Depending on the requirements and on material properties, the        diameter d_(h) of the bore can be chosen to approximately        correspond to a smaller diameter d₁ of the anchoring portion (if        defined; here the smaller diameter corresponds to the diameter        at axial positions where the grooves are) or to be smaller than        the latter or to be larger than the latter (but not larger than        the outer diameter d₂).

In the different embodiments described in this text, the distal tip 3 oredge as well as edges of the ribs or other protruding features of thecoupling structure serve as energy directors for the liquefaction of thethermoplastic material.

The embodiments described herein show a sonotrode 7 (or ‘horn’) as aseparate piece that is pressed against the proximally facing couplingface of the second object.

However, especially in embodiments in which the second object ismetallic, the second object may be a sonotrode directly coupled to avibration generating apparatus. It may, for example, be provided with aproximal thread or bayonet-coupling structure or similar for beingfastened to an according coupling of the vibration generating apparatus.

While the embodiments of FIGS. 1a -2 are assumed to have a rotationalsymmetry about the axis 10, this is not a requirement. Rather, it mayeven be advantageous to provide especially the anchoring portion with astructure that deviates from a circular symmetry, as discussedhereinbelow.

FIGS. 3a and 3b yet show an embodiment in which the second object 2 hasan inner portion 21 and an outer portion 22, with a gap 23 therebetween.The coupling structures are defined along an outer surface of the innerportion and/or an inner surface of the outer portion and/or an outersurface of the outer portion. In the depicted embodiment, the couplingsstructures (circumferentially running ribs that define grooves betweenthem) are present only along an outer surface of the inner portion.

When the second object is pressed into the first object whilethermoplastic material of the first object is liquefied, portions of theliquefied material flow into the gap (flow 11 in FIG. 3b ). In additionto anchoring the second object in the first object, this material will,after completion of the process, also stabilize the inner portion andthe outer portion with respect to each other.

The following options apply:

-   -   The inner portion and the outer portion may together be of one        piece, or they may be constituted by discrete pieces, like in        FIGS. 3a and 3 b.        -   In the latter case, they may optionally be made of different            materials. For example, if the second object is to be a            fastener for fastening something to the first object, the            inner portion may be of a metal, while the outer portion may            be of a lighter, less hard material, for example a plastic            material with a higher melting temperature (liquefaction            temperature) than the first object material. This includes            the possibility that the material of the outer portion is of            a material that is above its glass transition temperature at            the liquefaction temperature of the first object material so            that it is deformable, the deformation contributing to the            anchoring, as pointed out hereinbefore and explained in more            detail hereinafter referring to FIGS. 17a -20.        -   If the inner and outer portions are discrete pieces, they            may both reach to the proximally facing coupling face, or,            as in the depicted embodiment, only one of them reaches to            the coupling face. In the depicted embodiment, the            vibrations are coupled into the inner portion via the outer            portion.    -   Similarly to FIG. 2, a bore may be made in the first object        prior to the step of pressing the second object against the        first object. Such a bore may for example be made for the inner        portion only. Alternatively, it would also be possible to make a        bore with an inner bore portion and, for example, cylindrical        outer bore portion, for the respective portions of the second        object.    -   The inner portion 21 and/or the outer portion 22 may be        rotationally symmetric about an axis (the insertion        axis/anchoring axis), or its structure may deviate from such        symmetry.    -   Also the embodiment of FIGS. 3a and 3b can be carried out with a        bore in the first object, similarly to the bore 20 illustrated        in FIG. 2. The diameter of the bore can be chosen to be adapted        to the dimensions of the core portion 21, in accordance with the        discussion of FIG. 2 hereinbefore.

While the first and second portions 21, 22 in the embodiment of FIGS. 3a/3 b are shown to be pre-assembled, generally in embodiments with twoportions that are not of one piece, the portions may be assembledin-situ, for example by material of the first object connecting theportions and/or material of the second portion that has becomedeformable during the process or by other features.

In FIGS. 3a /3 b, the portions are assembled prior to being anchored,and the flow portion fills the gap 23 between them, with the effect ofyielding an additional bonding stability between the portions 21, 22.

For a gap between an inner portion 21 and an outer portion 22, a minimalwidth of 0.1 mm should be present in order for the thermoplasticmaterial to be capable to flow into.

FIG. 4a depicts, in a view, an embodiment in which the second object hasa metallic inner portion 21, for example of steel, and an outer portion22 of a plastic, for example of PEEK. The embodiment of FIG. 4a has thefollowing features that can be present together but that can also berealized individually or in combinations.

-   -   The central portion has a tube section extending from the distal        end (this includes the possibility of it being entirely tube        shaped).        -   The central portion includes an inner thread 26 or other            structure. If the tube section extends to the proximal end,            the inner thread may also extend to the proximal end and may            serve after the anchoring for mounting a further object to            the second object.    -   The coupling structure of the inner portion is not rotationally        symmetric but includes axial channels 24 that may direct the        material flow.        -   In embodiments, such axial channels 24 are deeper than the            circumferential grooves 5 with which the positive-fit            connection is caused, so as to serve as material            distribution channels.    -   The outer portion 22 is not circularly symmetric but includes a        plurality of outer axial protrusions that distally end in an        edge or tip.

The embodiment of FIG. 4a is an example of an embodiment in which thesecond object forms a proximal body (or head portion) 29, with distalprotrusions extending therefrom. The distal protrusions in the depictedembodiment are formed by leg-like extensions 28 (outer protrusions) andthe distal part of the first portion 21 (inner protrusion);configurations with a circumferentially running, for example skirt-likeouter protrusions are possible also.

In the hereinbefore described embodiments, the second object is anchoredin a depth-effective manner by providing the second object with ananchoring portion that extends along the anchoring axis, and in someembodiments with the aid of a bore in the first object. Theseembodiments may have a plurality of structure elements (the grooves 5,for example) into which liquefied material of the first object may flow,which structure elements are spaced axially from each other, such asarranged along a shaft and/or tube or similar.

In the variant of FIG. 4b , the metallic inner portion 21 ispre-assembled with the plastic outer portion 22. To add stability tothis pre-assembly, the structures 4 of the inner portion 21 extendproximally into the region of the proximal body 29 and are cast intomaterial of the outer portion 22.

After the process of bonding the second object 2 to the first object 1,the effective height h of the proximal body 29 is higher than itsinitial physical axial extension, because the flow portion of thethermoplastic material has filled the gap 23 between the inner and outerportions (backflow) (FIG. 4c ). A certain backflow will also take placeinto the central opening of the inner portion 21 if such centralopening, as illustrated, is open to the distal side. If such backflow isto be prevented, the opening may be closed off distally, for example bya tip-shaped end element.

The situation after the process as shown in FIG. 4c illustrates nicelyhow the outer portion 21 serves as mounting piece for a further object,with the outer portion 22 replacing a prior art mounting flange, whereinthe outer portion can be of a lightweight, low-cost material and stilladd substantial mechanical stability to the connection, especially withrespect to angular momenta on an object fastened to the inner portion 21(thread 26).

If necessary, additional stability with respect to axial forces may beprovided if the outer portion is provided with inner structures (groovesor similar) that are embedded by the flow portion of the thermoplasticmaterial to yield another positive-fit connection.

In the configuration depicted in FIGS. 4b and 4c , the distal ends ofthe inner portion 21 and of the protrusions 28 of the outer portion 22are depicted to extend to an approximately same axial depth (the bottomline is illustrated to be at equal height). This is not a requirement.Rather, the axial extensions of the inner protrusion formed by the innerportion 21 and of the outer protrusion/outer protrusions may generallybe chosen independently of each other, depending on requirements. Forexample, the inner portion 21 may extend further than the outerportion's protrusion(s) 28, or it may extend less far than the latter.

It may in special embodiments extend to not even reach the plane definedby the proximal surface in the assembled state (FIG. 4c , the planereaching the bottom of arrow h) so that it is not pressed into the firstobject but is only embedded in flowable thermoplastic material that hasflowed towards proximally due to the pressing force (backflow of theflow portion).

FIG. 4d yet shows a variant in which the first (inner) portion 221 doesnot reach to the distal end of the second object. Rather, the secondportion 222 of the plastic material includes both, at least one distalprotrusion 28 and at least one inner (central) distal protrusion 27. Asin the previous embodiments, the second object may be circularlysymmetrical with respect to rotations around the axis 10 or may havediscrete distal protrusions (such as shown in FIG. 4a ).

The embodiment of FIGS. 5a and 5b , in contrast, is suitable foranchoring the second object with respect to the first object also if thefirst object is flat. To this end, the second object includes aplurality of structure elements for the liquefied material to flow into,which structure elements are spaced laterally from each other, i.e.extend along a plane which during the anchoring is parallel to a surfaceplane of the first object. At least some of the structures elementsdefine an undercut.

More in particular, in the embodiment of FIGS. 5a and 5b , the secondobject includes a plurality of indentations 35 that in cross sectionhave the shapes of circular segments with a central angle of more than180° so that an undercut is generated. The indentations 35 may extend asgrooves along the plane perpendicular to the drawing plane, or they maybe present in other shapes and configurations.

As illustrated in FIG. 5b , the step of pressing and coupling vibrationsinto the tool will cause liquefaction to set in superficially at theinterface between the first and second objects, whereafter liquefiedthermoplastic material will flow into the indentations and thereby, dueto the undercut, fasten the second object to the first object afterre-solidification.

Yet another optional feature of this embodiment and of other embodimentsof the invention is schematically illustrated in FIG. 5b . When thesecond object is pressed against the first object, a counter force hasto act on the first object. In many embodiments, this counter force willbe exerted by a non-vibrating support on which the second object isplaced, such as by a working table or floor or dedicated support. Such anon-vibrating support will in many cases be arranged such that theportion of the first object that is immediately underneath the secondobject (more in general, the portion of the first object that extendsdistally from the interface between the first and second objects) issupported. However, this need not be the case. In FIG. 5b , the supportstructure 41 is such that immediately underneath the second object thereis no support for the first object, i.e. the distal side of the firstobject is exposed. This may be advantageous in situations where thedistal surface of the first object has a well-defined shape or otherproperties that must not be affected by the bonding process.

The feature of having the distal surface of the first object distally ofthe interface to the second object exposed is independent of the otherfeatures described referring to FIG. 5b , i.e. it may be implementedalso in other embodiments, and the embodiment of FIGS. 5a and 5b mayalso be carried out in an arrangement in which the distal surface issupported.

In the embodiment of FIGS. 5a and 5b , being an example of a planarbond, the depth d_(i) of the intermixing zone is larger than thepenetration depth d_(p) by which the second object penetrates into thefirst object. This nicely illustrates the fact that these embodimentsare, among others, especially suited for bonding a second object to aflattish first object or other object on which depth-effective anchoringis not possible. Nevertheless, also these embodiments do not feature thehereinbefore discussed disadvantages of adhesive bonds.

The width w of the bond/of the intermixing zone in embodiments of aplanar bond in at least one lateral dimension and often in both lateraldimensions is substantially larger than the penetration depth, thisbeing a further possible characteristic of planar bonds.

With respect to FIGS. 6a-6d yet a combined bonding process is described.The second object 2 is assumed to have a shape similar to the onedescribed referring to FIGS. 1a -2 with an anchoring portion including aplurality of protrusions and indentations between the protrusions. Thesecond object includes a thermoplastic material with a liquefactiontemperature substantially higher than a liquefaction temperature of thefirst object. For example, the second object may be made of PEEK, whilethe first object is made of PBT or Polycarbonate.

The first object includes a through bore 20 in which the second objectis anchored.

To this end, in a first stage, illustrated in FIG. 6b , the secondobject is pressed against the first object while mechanical vibrationsare coupled into it, until liquefaction of thermoplastic material of thefirst object sets in, so that the second object is advanced towards thedistal directions, while a flow 11 of thermoplastic material of thefirst object into the indentations 5 of the second element takes place.

The support 42 against which the first object is placed in thisembodiment includes a mould portion that forms a cavity 44 when thefirst object abuts against the support. The second object is providedwith an excess length so that at some stage of the process, before adistally facing stop face of the head portion 6 abuts against the firstobject, the distal end of the anchoring portion abuts against thesupport 42. Thereafter, the pressing force and the mechanical vibrationsare further applied and possibly intensified until also thermoplasticmaterial of the second object 2 becomes flowable (flow 51 in FIG. 6c )and fills the cavity. This will result in the second object being bondedto the first object by an additional rivet effect (FIG. 6d ) by way ofthe head portion 6 and a foot portion 52

The fact that thermoplastic material of the first object has flowed intostructures of the second object in addition to contributing to theanchoring also causes a sealing effect.

While in the embodiment of FIGS. 6a-6d and in other embodiments, thefirst and second objects are both assumed to be essentially homogeneous,this need not be the case. Rather, the first and/or second object may bea hybrid including portions of different materials. For illustrationpurposes, FIG. 7a depicts an embodiment in which a second object 2, forexample to be bonded to a first object in a process as illustratedreferring to FIGS. 6a-6d , includes a metal portion 61 and a distalplastic portion 62, for example of PEEK.

In the variant shown in FIG. 7b , the distal plastic portion 62 is asheath element connected to the metal portion 61 in a positive-fit likemanner. FIG. 7c illustrates the situation after the process, with adeformed part of the plastic portion 62 forming the foot portion 52, asillustrated hereinbefore.

Embodiments of the combined bonding process with the additional riveteffect are also especially suited for bonding a further object to thefirst object, with the rivet-like connector constituted by the secondobject securing the first and further objects to each other, asexplained referring to other embodiments in more detail hereinafter.

FIG. 7d yet illustrates that a hybrid second object 2 with a metallicportion 61 and a plastic portion 62 may also be suitable as a connectorin processes of the kind described hereinbefore, for example referringto FIGS. 1a-1d or 2.

FIG. 8 shows a further embodiment of a second object 2. Similarly to thetwo-piece embodiment of FIGS. 3a and 3b , it includes an inner part 21and an outer part 22 between which the thermoplastic material of thefirst object may flow. More in particular, the inner part 21 isshaft-like with outer structures 4, 5 that form an undercut with respectto axial directions. In addition or as an alternative, the outer part 21has inwardly facing structures, such as the depicted groove 71 formingan undercut.

In the depicted embodiment, the second object is of one piece formingthe inner and outer parts 21, 22. The gap 23 in embodiments like 4 a, 4b, 4, 8 and others may be viewed as opening open to the distal sideencompassing the central protrusion 21.

Compared to embodiments with just one pin-shaped shaft, the embodimentswith an inner portion and an outer portion due to the interplay betweenthe inner and outer portions bring about additional anchoring stability,especially if the thermoplastic material of the first object iscomparably soft or thin or brittle.

In the embodiment of FIG. 9, the second object 2 includes a body 73 of,for example, solid metallic material, and an interpenetration piece 74of an open porous material, such as metal foam or a metal mesh. Theinterpenetration piece is fastened to the solid metallic material. Thebody 73 forms at least part of the proximally facing coupling-in face,and the interpenetration piece 74 forms at least a part of the surfaceportion that is brought into contact with the first object. Due to theeffect of the mechanical vibration and the pressing force, thethermoplastic material penetrates into the interpenetration piece andthat due to its open porous structure forms undercuts and thus forms thecoupling structures.

The embodiment of FIG. 10 is an example of an embodiment with aninwardly facing coupling structure. More in particular, the secondobject 2 has an undercut indentation 35 into which the thermoplasticmaterial penetrates. An outer distal tip or edge 3 serves as energydirector. Due to an outward bend of the distal edge 3, the outer surface75 of the second object also forms a coupling structure with an undercutwith respect to axial directions. The embodiment of FIG. 10 is anexample of the principle described referring to FIGS. 5a and 5b with thedepth of the intermixing zone exceeding the penetration depth beingapplied to an element for a point connection instead of a flattishconnection.

FIG. 11 shows an alternative embodiment of a flattish connection withthe depth of the intermixing zone exceeding the penetration depth. Theembodiment is an example of an embodiment that is optimized for aflattish connection to a first object in which the impact of theconnection is to be minimized, for example because surface portions towhich the second object 2 is not directly attached (distal surfaceportions and/or proximally facing surface portions around the secondobject) need to maintain a certain quality. The bonding principle, likein FIG. 5a /5 b, is based on undercut indentations 35. The followingmeasures are implemented in the embodiment of FIG. 11:

The second object 2 includes protruding structures 36 with distal edgesor tips 3 that serve as energy directors and cause a swift onset of theliquefaction around the protruding structures.

A volume V₁ of the protruding structures is smaller than or equal to avolume V₂ of the indentations (see FIG. 12) into which the thermoplasticmaterial may flow. The separation depth between the volumes V₁, V₂(dotted line in FIG. 12) in this is defined to correspond to the depthby which the second object is inserted into the first object, i.e., thedotted line corresponds to the level defined by the proximally facingsurface of the first object. By this measure, it is assured that for allportions of thermoplastic material that are displaced by the protrudingportions, there is a space to flow to in the immediate vicinity. Thus,the method works with minimal material displacement and hence minimalheat flow.

The indentations and protrusions are arranged immediately next to eachother. I.e., there is no distance e (FIG. 13) between the protrusions 36and the indentations 36, or such distance is minimal. Also by thismeasure, material flow and thus heat flow is minimized.

In the embodiment of FIG. 11, the shown structures may extendcylindrically perpendicularly to the drawing plane. Alternatively, theindentations or the protrusions may be circular or have another shapeconfined in both lateral dimensions, and be arranged in a pattern overthe surface. For example, the second object may have a regulararrangement of dome shaped (especially spherical dome shaped)indentations, each surrounded by a ridge shaped protrusion. Or themountain-like protrusions could form a pattern, with groove-likeindentations between them. Also segmented and other arrangements arepossible.

FIG. 11 also illustrates that by the depth of the intermixing zone beinggreater than the penetration depth, in the region of the bond to thesecond object, an effective thickness d_(eff) is enhanced compared tothe real, physical thickness d of the object.

In the embodiment of FIG. 11, due to the tip or edge shaped protrusions,a relatively large depth is required for the anchoring. In alternativeconfigurations a compromise between the energy directing effect of edgesor tips and the requirement of smaller depth can be made, for example byusing rounded protrusions 36 as sketched in FIG. 14.

Also other cross sectional shapes may be feasible, including more edgyshapes as illustrated in FIG. 15. Such shapes may, depending on thechosen manufacturing method, be easier to manufacture by methods such ascutting or milling. More generally, manufacturing of the first objectmay include material removing methods as well as casting methods, or, asmentioned, the use of open porous structures.

In contrast, for example, to second objects 2 of the kind illustrated inFIG. 11, the energy impact and required pressure are higher for secondobjects as shown in FIG. 5a or also in FIG. 16 with a generally flatdistal end face 81. Objects of this kind are especially suited foranchoring in very thin first object (such as organo sheet material). Thebond is optimized for maximum strength per penetration depth, whereasgenerally the impact of the bonding process of the first object ishigher than in the embodiments of FIG. 11 and others.

In the hereinbefore described embodiments, the coupling structures thatinclude an undercut with respect to axial (proximodistal) directions andthereby make a positive-fit connection possible are pre-manufacturedproperties of the second object. Hereinafter, embodiments where thisform lock structure is formed during the process by deformation aredescribed.

FIG. 17a depicts a basic embodiment of this principle. The second object2 includes a main portion 90 and a plurality of deformable legsextending distally of the main portion 90. The material of the secondobject may be such that plastic deformation of the legs and/or elasticdeformation of the legs is possible. In embodiments, the second objectis made of a metal, with the legs being sheet portions of a thicknesssufficiently thin to make deformation under the conditions that applyduring the bonding process possible. Alternatively, the second objectmay be of a polymer-based material with an appropriately chosen contentof a reinforcement, or of any other suitable material or agglomerate.

FIG. 17b depicts the second object 2 anchored in the first object 1. Thelegs 91 upon insertion under the impact of the mechanical energy andpressing force are deformed to be spread outwardly, thereby afterre-solidification yielding the coupling structures.

FIG. 18 shows an embodiment that combines the principles of theembodiments of FIGS. 3 a/b and 17 a/b. In addition to including an outerportion 22 with a deformable portion 91 (deformable leg or otherdeformable structure), the second object also includes an inner portionthat in the shown embodiment is not deformable.

FIG. 18 also illustrates two further principles that are applicableindependent of the configuration of FIG. 18.

Firstly, the method in embodiments further includes pressing a retainingdevice 93 against the proximal face of the first object in a vicinity ofthe second object while the second object is bonded to the first object(in FIG. 18 the retaining device is shown on the left-hand side only,but it may also fully surround the second object). By this, bulges orthe like caused by pressing the second object into the first object(c.f. FIG. 1b /1 c) are avoided.

Secondly, similarly to the embodiments of FIGS. 5, 10, 11 and others,the process may be carried out to cause a backflow of material into theinterior space of the second object, here the space between the innerand outer portions. Thereby, the proximal-most portions of thethermoplastic material that has flowed during the process is proximallyof the initial proximal end face. This backflow, as describedhereinbefore, enhances the effective anchoring depth. In embodiments, aretaining device 90 of the described kind may assist the process in thata pressure is maintained around the second object, and the backflow iscaused to be within the interior space/cavity instead of around it. Thequantity Δh shown in the figure shows the difference by which thematerial has flowed inside relative to the proximal end face around thesecond object, and this quantity Δh may also correspond to the enhancedeffective anchoring depths.

FIG. 19 shows an example of an embodiment in which the support 42against which the assembly of the first and second objects are pressedby the sonotrode 7, has a shaping feature that assists the deformationof the deformable portion of the second object 2. More in particular, inthe embodiment shown in FIG. 19, the support 42 has a shaping protrusioncooperating with a corresponding indentation of the first object 1. Theshaping protrusion is of a material that is not liquefiable and does notsoften during the process. Also, possibly the support including theprotrusion 46 or other shaping feature may have a cooling effect, forexample by being actively cooled, so that the first object materialremains hard at the interface to it. Thereby, the deformable section isguided in the deformation process, to project away from the shapingfeature, as shown in FIG. 19. More in particular, the deformable legsthat constitute the deformable section are caused to be bent outwardlyaway from the shaping protrusion 46.

FIG. 20 shows an alternative embodiment where the shaping featureincludes a shaping indentation 44, so that the deformable legs arecaused to be bent inwardly into the configuration shown in FIG. 20.Various other alternatives are possible.

Generally, the second object may have the purpose of serving as ananchor for a further object to be attached to the first object, or mayitself be such a second object (in the above figures, the first objectare illustrated without any functional structures for such purpose,however, any such structures such as fastening structures or otherfunctional structures are possible.

Hereinafter, embodiments in which a further object (“third object”) isbonded to the first object in the bonding process by bonding the secondobject to it, are described.

FIG. 21a depicts a basic configuration. The second object 2—serving as aconnector in the embodiments in which the first object is bonded to afurther, third object—is depicted to be similar to the connector of FIG.1a without a head portion. Alternatively, other shapes of second objectsare possible; especially all objects described in this text suitable fordepth-effective anchoring, including second objects with a head portion,may be used. The third object 100 is shown as thermoplastic body,similar to the first object 1. It lies against the proximal face of thefirst object 1. For bonding, the second object 2 is driven both, throughthe third object 100 and the first object to be anchored in both, thefirst and third objects, as illustrated in FIG. 21 b.

The third object may include a thermoplastic material capable of beingwelded to the thermoplastic material of the first object 1. For example,it may be of a thermoplastic material with a same polymer matrix. In aregion around the second object, due to the liquefaction caused in theprocess a weld may be caused, as indicated by the circles 101. More ingeneral, material of the third object in the process is pressed into thefirst object to contribute to the connection after re-solidification.This also holds if the materials of the first and third objects cannotbe welded because they do not mix in the liquid state.

In addition or as an alternative to being driven through material of thethird object, the second object (connector) may also be driven through apre-made opening of the third object for its distal portion to beanchored in the first object. Such a pre-made opening may have adiameter allowing the second object to reach through it substantiallywithout resistance (see an embodiment described hereinafter) or mayencounter substantial resistance so that mechanical energy is absorbedalso there.

FIG. 22 shows a variant of a second object 2. This variant is distinctfrom the previously described embodiments in that it has a compressingstructure caused by a distally facing concave portion 111. This portionwill cause thermoplastic material of the third object 100 to be pressedinto the first object 1 yielding a more pronounced intermixing and, ifapplicable, weld, between the materials of the third and first objects.

FIG. 23 shows a further example of a second object 2 suitable as aconnector in the described sense. Especially, the second object 2according to FIG. 23 is particularly easy to manufacture and may beproduced as low-cost article. More in particular, the second objectincludes sheet portions for example of metal. The sheet portions form aplurality of legs 112 with barbs 113, all legs extending from a bridgeportion 114 and being one-piece with it. The second object may bemanufactured from a punched metal sheet by merely bending the legs awayfrom the bridge portion 114 and bending the legs 112 to have the barbs113.

Similarly, the embodiment of FIGS. 24a and 24b has a head portion 114(or bridge portion) with a plurality of legs extending therefrom. FIG.24a shows a punched-out metal sheet as intermediate piece, and FIG. 24bdepicts the second object 2 obtained by deforming this intermediatepiece through bending. The legs may be provided with beads or grooves(the same holds for FIG. 23) for additional stability.

In this embodiment, instead of the barbs, the legs 112 have distal arrowportions 115. Combinations would be possible.

A further, optional feature that does not depend on the legs isconstituted by a central hole 116 that may be used for guiding duringthe assembly process, for example together with a collar 117. Other usesof such a hole and/or collar are possible, including the fastening of afurther object to the second object.

FIG. 25 shows a second object that is formed by a perforated metalhollow cylinder 121. The perforations 122 of the metal cylinder may beinterpenetrated by thermoplastic material in the process and therebyensure the positive-fit anchoring. To minimize proximal heating, thevolume portion of the perforation might advantageously be close to orhigher than 50%.

The second object of FIG. 26 includes a metal mesh 125 also formed intoa hollow cylinder. The functioning principle is similar to the one ofthe hollow cylinder, with the meshes serving for interpenetration by thethermoplastic material.

Instead of being formed into a hollow cylinder, a perforated metal sheetor a mesh may be brought into other shapes for constituting a connectorof the described kind. FIG. 27 very schematically illustrates a spiralshape as an option.

A further option in addition to cylindrical (FIGS. 25 and 26) and spiralshaped in which the material is stable is wave-shaped, for exampleextending along a length dimension. An amplitude of such a wave may beat last 5-10 times the thickness of the sheet or mesh.

An even further variant is a square (in cross section perpendicular tothe axial direction) or other closed or open shape with a curve orbuckling.

Second objects having structures as the ones described referring toFIGS. 22-27 as well as referring to FIG. 37 hereinbelow may generally bevery thin and therefore sensitive to buckling. To this end, depending tothe application, a proximal connector structure may be advantageous toprovide stability.

FIG. 28 shows a cap 141 with a groove 142 for serving as proximal bridgeof a second object 2 with a spiral-shaped metal sheet or mesh to givethe second object additional mechanical stability during the process.

Second objects with thin structures as the ones described referring toFIGS. 22-28 as well as referring to FIG. 37 hereinbelow are suitable forfixation also in relatively thin first objects, with rather minimalenergy input. Because of their thinness a very small volume isdisplaced, and the melting zones will be very local. This minimizes theoverall pressure and the overall energy input.

Second objects 2 as connectors of the kind described referring to FIGS.22-28 may especially be suitable for fastening a first and a thirdobject together in a staple-like or pin-like manner, by the process asdescribed herein. In this, the way the first and third objects arearranged relative to one another with respect to the proximodistalanchoring axis may be varied, especially, it is also possible to pressthe connector through the first object into the third object instead ofthe other way round.

FIGS. 29a and 29b show a special application of the principle of using aconnector to connect a third object 100 to a first object 1. The secondobject is assumed to have a hat-like shape with a circumferentialprotruding section 131 extending distally from a main body 132.

In this special example, the third object 100 includes a foam that byinsertion of the second object 2 is compressed (compressed portion 102).Optionally, the second object may include relaxation openings 133 orother shape features that allow compressed material to flow away in casethe foam has thermoplastic properties (which is not necessary). FIG. 29billustrates corresponding flow-out portions 103.

While FIGS. 29a and 29b illustrate fastening of a foam material thirdobject, similarly a third object of another material may be fastened bythis approach, for example a soft and/or elastomeric material capable ofbeing cut through by the distal structures of the second object or anobject provided with a pre-manufactured bore for these structures.

In the embodiment of FIG. 30, the third object 100 is provided with abore 109 through which the distal portion of the second object may beadvanced to be brought into contact with the first object. In this, thethird object 100 may be thermoplastic, and the bore 109 may beunder-dimensioned in relation to the second object so that insertionthereof encounters resistance, and material of the third object aroundthe bore 109 is displaced. Alternatively, the third object may be of anot liquefiable material. Then, the bore 109 needs to be dimensioned sothat the distal portion of the second object fits through it or thedistal tip or a distal edge cuts through the third object material.

The second object in the depicted embodiment includes a resilient barbstructure 118 that allows pushing the distal portion of the secondobject through the bore 109 but that ensures anchoring in the firstobject 1 after liquefaction and re-solidification. The second objectalso has a proximal head portion 6 for securing the third object 100against the first object 1.

As an alternative to having a resilient barb structure 118, the secondobject in a configuration like the one of FIG. 30 could also have ashape similar to the one of FIG. 1a , again with a proximal head portion6, as for example shown in FIG. 31.

FIG. 32 depicts an embodiment in which a second object 2, for examplebeing entirely metallic, is anchored in a through opening 20 of thefirst object. The through opening narrows towards the distal side (iscountersunk), and the second object is accordingly tapered to beanchored around the opening. The first object 1 is assumed to be athermoplastic sheet.

The bond of the second object to the first object is a flattish bond,similar to the one taught with respect to FIGS. 5a /5 b; 11 and others,with structures for the interpenetration formed by sharp protrudingstructures 36 and indentations 35—even though the bonding surface of thesecond object is not planar but conical.

FIG. 33 shows an alternative where the through opening 20 of the firstobject is not tapered but stepped, with the fastening surface thatincludes the protruding structures 36 and the indentations 35 beinganchored around the step.

According to yet another alternative, illustrated in FIG. 34, if thesecond object 2 is allowed to protrude above the proximal surface of thesheet-like first object 1, a head-like proximal extension 6 of thesecond object may have a distal end face that includes the structures35, 36 to connect the second object to the rim of the opening.

In the variant of FIG. 35, for a configuration otherwise similar to theone of FIG. 32, two optional further features are realized (the featuresmay be realized independently of each other, with advantages if they arecombined):

-   -   The size of the structure elements 35, 36 decreases towards the        distally.    -   The opening angle α of the taper of the second object is greater        than the opening angle β of the taper of the through opening 20,        whereby the second object penetrates further into the first        object at more peripheral, proximal locations than at more        central, distal locations.

Both measures have the effect that more energy is absorbed and morematerial is liquefied at more proximal, peripheral locations than atmore distal, central locations around the opening. The effect is thatthe distal surface of the first object is kept intact.

FIG. 36 shows a variant of the embodiment of FIG. 11 in which, however,the structure elements that cause the bonding are restricted to theperiphery of the second object 2. In more central positions, the distalsurface 151 serves as a stop and abutment surface and thereby preciselydefines the axial relative position. In this, the considerations of FIG.12 concerning the relative volumes of the protruding structures 36 andthe indentations 35 may be particularly advantageous.

FIG. 36 is thus a very schematically illustrated example of anembodiment in which a connection zone between the first and secondobjects only constitutes a portion of their mutual interface. In otherportions of the interface, essentially no energy is transferred, and noliquefaction will take place.

In the embodiment of FIG. 37, protruding structures 161 for beinganchored in the second object are attached to a main body of the secondobject and protrude distally in directions essentially parallel to theaxial direction. The protruding structures may, for example, be formedsimilar to the structures illustrated in FIGS. 23, 24 b, 25, and 26 andbe particularly simple and cost efficient to manufacture.

In order to be stable with respect to buckling, the metal sheet or meshmay extend in a curved shape (for example, by forming a cylinder) orwave shape (perpendicular to the drawing plane) or other non-straightshape, as described hereinbefore.

In an example, the main body of the second object 2 may be of aliquefiable material (liquefiable at a same temperature as thethermoplastic material of the first object, at higher temperatures, oreven at slightly lower temperatures), with the protruding structures 161cast into them. In embodiments, a porosity of the structures may be atleast 50%.

1. A connector for being secured to a first object that comprises athermoplastic liquefiable material in a solid state, the connectorcomprising: a connector body defining distal end face and a proximal endface; the connector body defining a proximally facing coupling-instructure for being contacted by a tool that couples mechanicalvibration energy into the connector body; the distal end face extendinglaterally with respect to a proximodistal anchoring axis, the distal endface being equipped to be pressed against the first object for theconnecting element to be secure thereto while the mechanical vibrationenergy impinges on the connector body for causing a flow portion of thethermoplastic material of the first object to become liquefied and toflow relative to the connecting element body; wherein the distal endface comprises a plurality of laterally spaced openings, the openingsbeing shaped to receive a flow of the thermoplastic material; whereinthe laterally spaced openings each define an undercut structure withrespect to proximodistal directions, whereby the thermoplastic material,after re-solidification, secures the connector to the first object by apositive-fit connection between the undercut structure and thethermoplastic material; the connector further comprising a mountingstructure for securing a further object to the first object.
 2. Theconnector according to claim 1, wherein the laterally spaced openingsare cavities open towards distally.
 3. The connector according to claim2, further comprising protrusions between the cavities.
 4. The connectoraccording to claim 3, further comprising a distal surface portiondefining a separation plane, wherein a volume of the protrusions issmaller to or equal to a volume of the cavities, with respect to theseparation plane.
 5. The connector according to claim 1, wherein theconnector body forms distal edges extending along the openings, theedges serving as energy directors.
 6. The connector according to claim5, wherein the energy directors are formed by distally protrudingstructures extending along the openings.
 7. The connector according toclaim 6, wherein the protrusions are ridge shaped.
 8. The connectoraccording to claim 1, wherein the mounting structure comprises anundercut mounting structure being undercut with respect to proximodistaldirections, whereby thermoplastic material of the further object iscapable of flowing relative to the undercut mounting structure, andafter re-solidification, to secure the further object to the connectorand thereby to the first object by a positive-fit connection.
 9. Theconnector according to claim 1, wherein the distal end face comprises aplane portion without any indentations or protrusions, the plane portionbeing equipped to serve as a stop and abutment surface during theprocess of securing.
 10. A connector for being secured to a first objectthat comprises a thermoplastic liquefiable material in a solid state,the connector comprising: a connector body defining distal end and aproximal end; the connector body defining a proximally facingcoupling-in structure for being contacted by a tool that couplesmechanical vibration energy into the connector body; wherein theconnector body forms an inner distal protrusion and an outer distalprotrusion, and a distally facing opening that extends around the innerdistal protrusion and is located between the inner and outer distalprotrusions; wherein the outer distal protrusion has a couplingstructure forming an undercut with respect to proximodistal directions,whereby a flow portion of the thermoplastic liquefiable material flowsrelative to the outer distal protrusion towards proximally so as toembed the coupling structure, and after re-solidification of thethermoplastic material, locks the connector relative to the firstobject.
 11. The connector according to claim 10, wherein the couplingstructure of the outer distal protrusion comprises an inwardly facingcoupling structure facing inwardly towards the opening.
 12. Theconnector according to claim 10, wherein the inner distal protrusion hasan inner coupling structure forming an undercut with respect toproximodistal directions, whereby the flow portion of the thermoplasticliquefiable material flows relative to the inner distal protrusiontowards proximally so as to embed the inner coupling structure, andafter re-solidification of the thermoplastic material locks theconnector relative to the first object.
 13. The connector according toclaim 10, further comprising a mounting structure for securing a furtherobject to the first object.
 14. The connector according to claim 13,wherein the mounting structure comprises a thread accessible fromproximally of the connector body.
 15. The connector according to claim10, wherein the outer distal protrusion extends circumferentially aroundthe opening and has a plurality of distal extensions ending distally ina tip or edge.
 16. The connector according to claim 10, wherein thecoupling structure of the outer distal protrusion has at least onecircumferential groove.
 17. The connector according to claim 12, whereinthe inner coupling structure has at least one circumferential groove.